A magnification-type display device such as a projector is well known, which forms an optical image depending on a video signal on a light valve, and illuminates the optical image with light so as to magnify and project the optical image onto a screen with a projection lens, whereby a large screen video image is obtained.
In such a projection display device, when three light valves are used corresponding to light beams of three primary colors of red, green, and blue, a projected image with high brightness, high resolution, and satisfactory color reproduction can be displayed. Further, a plurality of light sources may be used to bring about the following advantages. That is, a projected image with higher brightness can be obtained, and even if one of the light sources does not illuminate due to a malfunction, the projected image can be displayed without interruption when the other light source illuminates. A projection display device using a plurality of light sources is disclosed in Patent Documents 1 and 2, for example.
FIG. 11 shows a configuration example of a projection display device with two light sources disclosed in Patent Document 2. In FIG. 11, light beams emitted from light sources 1a and 1b are focused on a light combiner prism 3 by ellipsoidal mirrors 2a and 2b, respectively. The light combiner prism 3, which has a reflecting mirror on its light incident surface, reflects the focused light beams from the ellipsoidal mirrors 2a and 2b as divergent light toward a side of the collective optical system including a focusing lens 11, so that their optical axes are close to each other, and the two light beams are synthesized and travel in the same direction along an optical axis 10 of a collective optical system.
The light from the light combiner prism 3 is converted into substantially parallel light by the focusing lens 11. The substantially parallel light from the focusing lens 11 is incident on a first lens array plate 12 composed of a plurality of lenses. The light beam incident on the first lens array plate 12 is split into numerous light beams, and the numerous light beams thus obtained are converged on a second lens array plate 13 composed of a plurality of lenses. On the second lens array plate 13, many minute images of the plurality of light sources 1a and 1b are formed.
Each of the lens elements of the first lens array plate 12 has a focal length equal to a distance between the first lens array plate 12 and the second lens array plate 13. The lens element of the first lens array plate 12 has an aperture in a shape similar to that of a liquid crystal panel 16. Each of the lens elements of the second lens array plate 13 has a focal length that is determined so that a surface of the first lens array plate 12 and a surface of the liquid crystal panel 16 have a substantially conjugate relationship.
An illumination lens 14 is provided for overlapping exiting light beams from the respective lens elements of the second lens array plate 13 on the liquid crystal panel 16 so that the liquid crystal panel is illuminated with the thus overlapped light beams. The numerous exiting light beams from the second lens array plate 13 are overlapped on the liquid crystal panel 16, so that the liquid crystal panel 16 is illuminated uniformly with high efficiency.
A field lens 15 is provided for focusing the light beams illuminating the liquid crystal panel 16 on a pupil plane 18 of a projection lens 17. The projection lens 17 projects an optical image formed on the liquid crystal panel 16 onto a screen (not shown).    Patent Document 1: Japanese Patent No. 3581568    Patent Document 2: JP 2000-171901 A